This invention relates to a lamination apparatus and in particular to a dual belt driven, continuous pressure lamination apparatus that utilizes pressure, heat and cooling to bond at least two substrates (plies) with an adhesive between the layers of the substrates. The laminator of the present invention overcomes many of the disadvantages of prior art laminators, including shrinkage of materials, and the like.
This invention relates to a lamination apparatus and in particular to a dual belt driven, continuous pressure lamination apparatus that utilizes pressure, heat and cooling to bond at least two substrates (plies) with an adhesive between the layers of the substrates.
The laminator of the present invention can be employed to make a variety of composite and/or reinforced materials. One or more of the component parts of the laminate (i.e., the substrates or plies) may be a woven fabric material, a non-woven fabric web, or a mat of fibers. Adhesive materials, preferably thermoplastic materials, are used to bond the various substrates in the laminate construct. These materials may be melted and remelted over and over. When used to laminate yarns, especially polymer yams, thermoplastic copolyester adhesives are preferred, as these materials may be selected to have a melting temperature below the melting temperature of the yarns. Industrial type laminates that may be formed using the laminator of the present invention include natural and/or synthetic fabric-based, asbestos-based, glass-based, nylon-based, flame-retardant and/or flame-resistant based, and mixtures thereof. Laminates of other materials may also be prepared as will be appreciated by those having ordinary skill in the field.
Non-woven fabrics are one especially preferred class of materials used as the plies or substrates in the pressure laminator of the present invention. Non-woven fabrics are similar to woven and knitted fabrics in that all are planar, inherently flexible, porous structures composed of natural or synthetic fiber materials (i.e., yarns, threads, or filaments). Non-woven fabrics are unique in that they can be engineered to resemble woven or knitted fabrics, but they can also be made to have superior physical characteristics over woven or knitted fabrics. Thus, non-woven fabrics are highly influenced by the properties of their constituent fibers and the manner in which the non-woven fabric is prepared. Typical methods for preparing non-woven fabrics include mechanical, chemical and thermal interlocking of layers or networks of the fiber materials.
In preferred embodiments, the substrates are at least two non-woven fabric substrates, one of the fabric substrate representing the weft strands and another representing the warp strands. The adhesive used to bond the nonwoven substrates should be activated by heat during the lamination process. The combination of pressure, heating to activate the adhesive and rapid cooling of the joined substrates minimizes shrinkage and sets the yarn size in the final non-woven fabric laminate. In addition, because the laminate is being formed under pressure, the warp and weft yarns are forced into intimate contact, giving the final laminate the appearance of a woven product.
The lamination apparatus of the present invention has an outer housing or frame in which a rectangular pressure box is mounted. The shape of the box need not be rectangular, but this shape is currently preferred. The pressure box comprises two spaced apart sections, an upper section and a lower section, each of which has pressure seals along its four edges, and each of which is further provided with a plurality of both heating and cooling elements. Two counter rotating drive belts, an upper drive belt and a lower drive belt, contact one another at and together run through a space between the two sections of the pressure box. The belts are dimensionally larger (length and width) than the pressure box. This is necessary to permit pressurization of the box, both above and below the two belts. One belt is driven in a clockwise manner and the other belt is driven in a counterclockwise manner. Once the belts are in motion, one end of the pressure box is the inlet (feed) end and one end is the outlet end of the laminator.
The lower section of the pressure box is mounted rigidly to the frame or housing, whereas the upper section of the pressure box can be adjusted as necessary to permit access to the interior of the box. Normally, the sections are spaced apart sufficiently to permit passage of the drive belts there through under pressure (or in a depressurized state), with or without material to be laminated there between.
During the lamination process, substrate materials to be laminated are passed through a pressure seal at the inlet end of the pressure box, and into the space between the two drive belts. Air pressure applied to the upper and lower sections of the pressure box is used to compress the air-impermeable belts toward one another, creating a diaphragm effect between the belts, thereby compressing the substrates situated there between. The upper and lower sections of the pressure box are equipped with a plurality of heating and cooling elements, which are used to activate and set the thermoplastic adhesive between the substrate layers.
In an especially preferred embodiment, the plurality of heating and cooling bars located in the lower section of the pressure box are rigidly mounted, whereas the plurality of heating an cooling bars in the upper section of the pressure box are mounted so as to float on top of the materials being laminated. This arrangement has been found to be especially useful in the preparation of non-woven fabrics. Shrinkage is minimized or eliminated and the final laminate has the physical characteristics (feel and appearance) of a thermomechanicaily finished fabric.
Advantageously, at least about 10%, preferably at least about 25% and most preferably about 50% of the box interior at the inlet end of the pressure box is provided with heat bars, and the remainder of the pressure box, again, at least about 10%, preferably at least about 25% and most preferably about 50% of the box interior, is provided with cooling bars. The heating bars are ideally located at the inlet end of the pressure box and the cooling bars are ideally located at the outlet end of the pressure box. If desired, multiple zones of heating and cooling could be included within the pressure box; e.g., heat/cool, heat/cool, heat/cool, etc.
Movement of the two belts through the pressure box allows for the continuous feeding of substrate materials and thermoplastic adhesive enter the laminator through an entry pressure seal. Once therein, the substrates are nipped or pressed together by the diaphragm effect caused by the pressure applied to the belts. The pressed substrates are then heated under pressure, melting the thermoplastic adhesive. This allows the substrate layers to come closer together, with at least some portions of the warp and weft yarn strands becoming coplanar or nearly coplanar. The heated substrates are then cooled, while still under pressure, forming the final laminate. The cooled laminate exits the pressure box through an exit pressure seal, where it is collected as desired.
When two or more non-woven polyester substrates (e.g., at least one warp substrate and at least one weft substrate) are laminated in this apparatus, the thickness of the laminate at the outlet end of the laminator is at least 5%, preferably at least 10% and most preferably at least about 20% less than the combined thickness of the substrates and thermoplastic adhesive, as measured at the inlet end of the laminator.
The current rectangular pressure has a pressure area about 1500 square inches (in2). The drive belts, which are substantially non-porous, are pressurized from both sides of the pressure box with air (or other fluid medium) pressure of at least 2 psi, preferably at least about 5 psi, and most preferably at least about 10 psi. Higher pressures can be achieved with modification of the equipment to support and sustain the same. This pressure applied to the belts is equivalent to a compressive weight (force) ranging from about 5000 lbs to about 50,000 lbs, applied over the 1500 in2 area of the current pressure box. For laminating non-woven fabrics, a compressive force from about 10,000 lbs to about 25,000 lbs is typical, and a compressive force of about 15,000 lbs (at 10 psi gauge) has been found to be especially preferred to date. This is important because in a traditional laminator, which uses top and bottom platens, if a weight of 15,000 lbs was placed on the top platen to provide the compressive force to effect lamination, any belt running hereunder would likely break. Traditional high pressure laminators usually employ a series of actions; move, stop, press; move, stop, press; etc., when operating in a xe2x80x9ccontinuousxe2x80x9d manner.
In the present invention, the use of a fluid pressure medium, e.g., air (or other gas, e.g., steam) or liquid (e.g., water, oil, etc), allows the belts to move, even though being pressured from both the top and the bottom. The belts of the present laminator slide through, even though they encounter forces that would break a belt in a conventional laminator.
This invention is also directed to a method of manufacturing non-woven fabrics using the pressure lamination apparatus, and to the non-woven fabrics formed thereby. The pressure laminator of the present invention has been specifically designed to permit the permanent joining of at least two non-woven fabric substrates with an adhesive between the fabric substrates, with little or no shrinkage occurring, during the lamination process. While not wishing to be bound by theory, it is believed that shrinkage is prevented or limited herein, due to the high pressure on the belts, which prevents the laminate from slipping, thereby preventing or limiting shrinkage. The resulting non-woven composite fabric advantageously has the appearance of a woven fabric, but has superior strength characteristics there over.
While designed for a specific purpose, the pressure laminator of the present invention can have other uses, for example, printed circuit board substrate manufacture, decorative laminating, industrial laminating, and the like, as will be appreciated by those having ordinary skill in this art.